An arrangement in which an arm main body of a suspension arm formed by press forming a metal plate has a cross-sectional shape having an open lower face formed from an upper wall portion, a pair of side wall portions formed by downwardly bending opposite side edges of the upper wall portion, and a pair of lower wall portions formed by inwardly bending the lower edges of the side wall portions, a reinforcing rib downwardly recessed along opposite side edges of the upper wall portion is formed, and a raised part projecting upward between the two reinforcing ribs is formed is known from Patent Document 1 below.
Furthermore, an arrangement in which a hollow suspension arm is formed by superimposing and welding outer peripheral parts of a first plate-shaped member and second plate-shaped member formed by press forming a metal plate, and a pipe member for supporting a rubber bush joint is fixed by welding to an end part on the vehicle body side of the suspension arm is known from Patent Document 2 below.
Moreover, an arrangement in which an arm main body of a suspension arm formed by press forming a metal plate has a cross-sectional shape having an open lower face formed from an upper wall portion and a pair of side wall portions formed by downwardly bending opposite side edges of the upper wall portion, and rigidity is enhanced by forming a concavo-convex shape in which recesses and projections are continued in front and rear side wall portions is known from Patent Document 3 below.    Patent Document 1: Japanese Patent Application Laid-open No. 9-123722    Patent Document 2: Japanese Patent Application Laid-open No. 9-20115    Patent Document 3: Japanese Patent Application Laid-open No. 2004-90750